Conventionally, there are known ultrasonic welding devices (for example, Japanese Patent Publication No. 3988835) for ultrasonically welding an object to be welded (web) to form disposable diapers, for example.
An ultrasonic welding device disclosed in Japanese Patent Publication No. 3988835 includes a drum having an outer surface configured to support an object to be welded that is continuously supplied, the drum being rotatable about a predetermined rotation axis, and a horn and an anvil attached to the drum to thereby revolve about the rotation axis and sandwich the object supported over the outer surface of the drum to ultrasonically weld the object.
When one of the horn and the anvil is defined as a first welding tool and the other of the horn and the anvil is defined as a second welding tool, the first welding tool is attached to the drum in such a manner as to be movable relative to the second welding tool so that the first welding tool can move across the object supported over the outer surface of the drum.
According to the ultrasonic welding device disclosed in Japanese Patent Publication No. 3988835, the drum rotates integrally with the horn and the anvil. Therefore, the rotation of the drum allows the object to be welded between the horn and the anvil while being conveyed.
Thus, the period of conveying the object can also be used as a period of welding, unlike the case where an object to be welded is fed into the space between a horn and an anvil secured at a position. Therefore, it is possible to obtain a sufficient welding strength while conveying the object at a high speed.
By the way, it is necessary to change the space between adjacent welding positions of the object, according to the design of a product such as size that is made of the welded object.
Here, in order to increase the space between adjacent welding positions, it is necessary to increase the circumference of the drum so that the circumference over which the object is welded by the welding tools is increased. On the other hand, in order to reduce the space between adjacent welding positions, it is necessary to reduce the circumference of the drum.
However, in the ultrasonic welding device disclosed in Japanese Patent Publication No. 3988835, the drum is used to support the object to be welded. Therefore, it is necessary to replace the drum to change the circumference of the drum.
Here, the drum is mounted with the anvil, the horn, and a structure for connecting these components to the drum. Therefore, there is a problem that the work of replacing the drum is very troublesome.